1. Field of the Invention
The present invention relates to an ink-jet head and a method of manufacturing the ink-jet head. The ink-jet head has an electrode formed on an inner surface of a diaphragm in an ink chamber, and a drive voltage is applied to the electrode according to image data to cause shear deformation of the diaphragm and accordingly cause a pressure change within the ink chamber. Ink drops are thus selectively ejected from respective ink chambers.
2. Description of the Background Art
Nonimpact printers such as ink-jet printer are appropriate for color printing and increasing number of gray-scale levels, and the nonimpact printers replacing impact printers have rapidly been widespread in recent years. A nonimpact printer of drop-on-demand type employs Kaiser method using a piezoelectric element or employs thermal jet method using a heating element for ejecting required ink only when a print is made. This drop-on-demand type printer is advantageous particularly in printing efficiency, production cost and running cost for example, and thus is in the mainstream of the nonimpact printers.
According to the Kaiser method, the volume of the piezoelectric element outside an ink chamber changes to deform a part of a wall forming the ink chamber so that ink is ejected therefrom. This Kaiser printer is difficult to decrease in size and inappropriate for enhancement of resolution. According to the thermal jet method, heating of the heating element causes air bubbles in the ink contained in an ink chamber and the pressure of the air bubbles causes ink to be ejected. The ink is repeatedly subjected to heating and cooling and thus the ink must have a high endurance, and the heating element has a short lifetime and a high power consumption.
In order to overcome these disadvantages, an ink-jet printer utilizes shear deformation of piezoelectric material forming an ink chamber, the shear deformation resulting in a change in pressure of ink within the ink chamber, and accordingly ink is ejected. In this type of ink-jet printer, a plurality of groove-shaped ink chambers partitioned by diaphragms are formed on a substrate of piezoelectric material, and a drive voltage is applied to an electrode formed on an inner surface of the diaphragm in the ink chamber to cause shear mode deformation of the diaphragm of piezoelectric material. Then, the pressure of ink which fills the ink chamber changes to eject ink drops from the ink chamber. The ink-jet printer of this type is suitable for increase in the density of nozzles, decrease of power consumption and higher frequency of the drive voltage.
Referring to FIGS. 6 and 7, a conventional ink-jet head formed of piezoelectric material includes a plurality of groove-shaped ink chambers 104 partitioned by diaphragms 103 that are formed on the upper surface of a substrate 101 of piezoelectric material which is polarized in the direction of thickness. The ink-jet head further includes a cover plate 102 where an ink supply opening 121 and a common ink chamber 122 to be placed on the upper surface of ink chambers 104, and a nozzle plate 109 where a nozzle 110 communicating with the front side of each ink chamber 104 is formed. Cover plate 102 and nozzle plate 109 are attached to substrate 101. An electrode 105 is formed on an upper half of the inner surface, in the direction of depth, of each diaphragm 103 in ink chamber 104.
Ink chamber 104 includes a shallow-groove region 106 on the back side of region A of a constant depth with region B therebetween. The bottom surface in the cross section of region B is in the shape of arc corresponding to the diameter of a dicing blade used for dicing for forming ink chamber 104 on substrate 101. Shallow-groove region 106 is used as a region for connecting the electrode electrically to an external driving circuit. An electrode 108 of a flexible substrate for example has one end connected to the external driving circuit, and the other end thereof is connected to electrode 105 formed on shallow-groove region 106 via a bonding wire or anisotropic conductive film (ACF).
In the conventional ink-jet head shown in FIGS. 6 and 7, the cross sectional bottom surface of ink chamber 104 in region B is in the shape of arc. In region B communicating with common ink chamber 122, the upper surfaces of diaphragms 103 are not joined to cover plate 102. Therefore, even if a drive voltage is applied to electrode 105, no shear deformation occurs in diaphragms 103 in region B and accordingly no pressure for ejecting ink is generated. In other words, region B is an unnecessary part which does not contribute to the essential ink-ejecting function. Rather, region B impedes shear deformation of diaphragms 103 in region A.
Formation of electrode 105 is also necessary in region B. Then, the capacitance of electrode 105 increases, which causes delay in rise and fall of a drive voltage and accordingly results in increase of power consumption. In addition, the length of region B in the direction from the front side to the back side of substrate 101 is determined depending on the diameter of the dicing blade used for dicing and on the depth of ink chamber 104. For example, if the dicing blade of 52 mm in diameter is used for forming ink chamber 104 of 360 xcexcm in depth, the length of region B is approximately 4.3 mm which is equal to or greater than the length of region A. Then, the material cost increases due to the increased area of substrate 101.
In order to eliminate the region in the ink chamber that is unnecessary for generation of pressure by which ink is ejected, an ink-jet head structure is proposed according to which the ink chamber has a constant depth over the entire length in the direction from the front to the back side of the substrate. Referring to FIG. 8 which is an exploded perspective view of such a structure viewed from the back side thereof, a cover plate 202 has no ink supply opening and no common ink chamber. Instead, a manifold 260 has an ink supply opening 261 and a common ink chamber 262 formed therein and is joined to the back side of a substrate 201. An electrode 205 is formed on an inner surface of each diaphragm 203 in an ink chamber 204. Respective electrodes 205 of ink chambers 204 are separately formed and continue to the back side of substrate 201 where the back end surfaces of diaphragms 203 are located. On the back side of substrate 201, electrodes 205 are electrically connected to an external driving circuit.
In this conventional ink-jet head, from which eliminated the region of the ink chamber that is unnecessary for generation of pressure causing ejection of ink, the electrodes are formed from the inner surfaces of diaphragms to the back surface of the substrate, the back surface being orthogonal to the inner surfaces. Therefore, it is likely that the electrode has an insufficient thickness at the right-angled corner where the inner surface of the diaphragm and the back surface of the substrate meet. When the ink-jet head is assembled, the electrode at the corner is readily separated by being touched or hit with another component. Consequently, the electrode is broken and no shear deformation can be caused in the diaphragm even if a drive voltage is applied thereto. A resultant problem is accordingly that ink cannot correctly be ejected.
One object of the present invention is to provide an ink-jet head and a manufacturing method thereof, the ink-jet head eliminating any region in an ink chamber that is unnecessary for generation of pressure which causes ink ejection while surely preventing an electrode from being broken, and being able to correctly ejecting ink according to a drive voltage.
The present invention is structured as detailed below for achieving the object above.
(1) According to the present invention, an ink-jet head includes a substrate of piezoelectric material and a plurality of groove-shaped ink chambers each having respective ends in the longitudinal direction that open respectively at front and back end surfaces of the substrate, the ink chambers being partitioned by diaphragms respectively and formed on an upper surface of the substrate, and the ink-jet head further includes an actuator portion having an electrode formed on an inner surface of each of paired diaphragms facing each other in each ink chamber, the electrode continuing to the back end surface of the substrate. Each diaphragm has a surface which forms an obtuse angle with the inner surface of the diaphragm in the ink chamber and forms an obtuse angle with a back end surface of the diaphragm, and the surface of the diaphragm is formed, in the direction of depth of the ink chamber, in a range including at least a region where the electrode is formed.
In this structure of the ink-jet head, the inner surface of each diaphragm in the ink chamber and the back end surface of the diaphragm are continuously formed through the surface which meets the inner surface with an obtuse angle therebetween and meets the back end surface with an obtuse angle therebetween, and the electrode is formed continuously on these surfaces. Accordingly, the electrode continues from the inner surface in the ink chamber to the back end surface of the diaphragm through the corner portion with angles greater than 90xc2x0. Then, the electrode has a sufficient thickness on the corner portion and is never readily broken even if being touched or hit with any component.
The surface of the diaphragm, which forms an angle greater than 90xc2x0 with the inner surface and forms an angle greater than 90xc2x0 with the back end surface, is formed in the direction of depth of the ink chamber in a range including at least a region where the electrode is formed. Accordingly, the inner surface and the back end surface continue to at least a part of the surface in the direction of depth of ink chamber, the surface forming an angle greater than 90xc2x0 with each of the inner surface and back end surface of the diaphragm. Therefore, the electrode has a sufficient thickness on the corner portion and is never readily broken even if being touched or hit with any component.
(2) The electrode on the back end surface of the substrate is divided into respective separate sections for respective ink chambers.
According to this structure, the electrode formed on the back end surface of the substrate is divided into respective sections for respective ink chambers. A drive voltage is thus applied individually to each of the electrode sections formed for respective ink chambers so that an image is formed with a resolution according to the intervals between the ink chambers.
(3) In the structure described in section (1) or (2), the electrode on the back end surface of the substrate can electrically be connected to an external driving circuit.
According to this structure, the minimum distance is achieved between the electrode on the inner surface in the ink chamber and a position where the electrode is connected to the external driving circuit. The capacitance of the electrode can thus be made minimum to reduce power consumption.
(4) A method of manufacturing an ink-jet head includes a grooving step for forming, on an upper surface of a substrate of piezoelectric material, a plurality of groove-shaped ink chambers each having respective ends in the longitudinal direction that open respectively at front and back end surfaces of the substrate, the ink chambers being partitioned by diaphragms respectively, and an electrode forming step for forming an electrode on an inner surface of each of paired diaphragms facing each other in each ink chamber, the electrode continuing to the back end surface of the substrate. The method further includes a surface processing step for forming, prior to the electrode forming step, a surface of the diaphragm that forms an obtuse angle with the inner surface of the diaphragm in the ink chamber and forms an obtuse angle with a back end surface of the diaphragm, the surface of the diaphragm being formed, in the direction of depth of the ink chamber, in a range including at least a region where the electrode is formed.
According to this method, after formation of the surface which forms an obtuse angle with the inner surface of the diaphragm in the ink chamber and forms an obtuse angle with the back end surface of the diaphragm, the electrode is formed to continue from the inner surface to the back end surface. Accordingly, the electrode continues from the inner surface in the ink chamber to the back end surface of the diaphragm through the corner portion with angles greater than 90xc2x0. Then, the electrode has a sufficient thickness on the corner portion and is never readily broken even if being touched or hit with any component.
The surface of the diaphragm, which forms an obtuse angle with the inner surface and forms an obtuse angle with the back end surface, is formed in the direction of depth of the ink chamber in a range including at least a region where the electrode is formed. Accordingly, the inner surface and the back end surface continue to at least a part of the surface in the direction of depth of ink chamber, the surface forming an angle greater than 90xc2x0 with each of the inner surface and back end surface of the diaphragm. Therefore, the electrode has a sufficient thickness on the corner portion and is never readily broken even if being touched or hit with any component.
(5) According to the method described in section (4), the electrode may be formed by vapor deposition of a material for the electrode.
According to this method, simultaneously with formation of the electrode on the inner surface in the ink chamber, the electrode is formed on the surface forming an obtuse angle with the inner surface and forming an obtuse angle with the back end surface of the diaphragm as well as on the back end surface of the substrate. Then, the manufacturing process can be simplified and accordingly the manufacturing cost can be reduced.
(6) The surface processing step is carried out prior to the grooving step, and the surface processing step includes the steps of covering an upper surface of the piezoelectric material with a mask member having an opening with a predetermined shape and performing sandblasting from an upper surface of the mask member.
According to this method, after the upper surface of the piezoelectric material, which is covered with the mask member having an opening with a predetermined shape, is sandblasted, the grooving step is performed for forming ink chambers. Then, prior to formation of the ink chambers, the sandblasting surely produces the surface which forms an obtuse angle with the inner surface of the diaphragm in the ink chamber and forms an obtuse angle with the back end surface of the diaphragm.
(7) The surface processing step is carried out after the grooving step for chamfering a corner formed by the inner surface of the diaphragm in the ink chamber and the back end surface of the diaphragm.
According to this method, after the grooving step for forming ink chambers, the corner formed by the inner surface and the back end surface of the diaphragm is chamfered. Then, after formation of the ink chambers, a cutting process such as milling is performed to surely produce the surface which forms an obtuse angle with the inner surface of the diaphragm in the ink chamber and forms an obtuse angle with the back end surface of the diaphragm.
(8) The method further includes the step of forming a mask member, prior to the electrode forming step, for dividing a back end surface of the diaphragms into respective separate sections for respective ink chambers.
According to this method, the back end surface of the diaphragms is divided into respective sections for respective ink chambers by the mask member before the electrode forming step. Then, after the electrode forming step, respective sections of the electrode for respective ink chambers are formed on the back end surface of the diaphragms. Therefore, no breakage of diaphragms occurs, the breakage being caused by any process distortion when the electrode is mechanically removed partially. Consequently, the yield is improved.
(9) The method further includes the step of removing, after the electrode forming step, a part of the electrode formed on the back end surface of the substrate to divide the electrode into respective separate sections for respective ink chambers.
According to this method, the electrode formed on the back end surface of the substrate in the electrode forming step is partially removed and accordingly divided into respective sections for respective ink chambers. In this way, the electrode formed on the back end surface of the substrate is separated at accurate positions and each ink chamber thus has uniform electrical characteristics maintained therein.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.